Synthesis of Some Vanillin Derivatives and their Use as an Optical … · 2009. 6. 7. · Fig. 6....

JKAU: Sci., Vol. 21 No. 1, pp: 117-128 (2009 A.D. / 1430 A.H.)

117

Synthesis of Some Vanillin Derivatives and their Use

as an Optical Sensor for the Detection of

Volatile Organic Compounds

Abdullah M. Asiri, Gameel A. Baghaffar,

Ali M. Al-Harby and Mohie Aldien M. Zayed

Chemistry Department, Faculty of Science,

King Abdulaziz University, Jeddah, Saudi Arabia

Abstract. Six new dyes derived from vanillin and active methylene

have been prepared and characterized using H-NMR, FT-IR spectral

data. These dyes were tested for use as sensors for volatile organic

compounds (VOCs namely Triethyl amine and diethyl amine). The

electronic spectra of these dyes was examined and gave color

depending on the acceptor groups. The compounds were tested to

sense organic amines such as diethyl amine and triethyl amine, all the

compounds tested gave color change from less color to deep color

which can be seen by naked eye, rendering these materials to be easy,

inexpensive sensor for volatile organic compounds which are basic in

nature.

Keywords: Vanillin, Sensors, Volatile organic compounds (VOC),

sensing amins.

Introduction

In recent years, the solid state gas sensors demand for safety control

requirements, environmental monitoring and food quality control has

expanded enormously. In particular the detection of volatile organic

compounds in low concentration, has become of interest, because they

are widely used as ingredients house-hold products. These compounds

vaporize at normal room temperature, sometimes causing adverse health

effects. Moreover, foods emit mainly low molecular weight alcohols and

esters, but also amines and aldehydes are present.

Abdullah M. Asiri, et al.

118

To this purpose the sensing elements necessary to monitor specific

gases or VOCs must demonstrate high selectivity feature. In the cases in

which the sensing element not shows the required selectivity, a

development of an array configuration becomes indispensable.

Consequently, a great interest on searching the solid state gas sensor with

high sensitivity, stability and wide selectivity spectrum has been

developed. In array configuration each sensing element must demonstrate

a broad selectivity range towards various kinds of volatile organic

compounds. But there is a research competition between the possible

realization of large number of sensors element disposed in array

configuration or the tentative to modify the sensing technique in order to

increase the selectivity of a specific sensitive material. In the first case

the increasing of the number of sensing elements leads to increase the

dimension of the system and the complexity of the sensing equipment.

The second approach consists in the modification of the sensing

technique, by minimizing the use of the sensing material. Different

transduction techniques are used for gases or VOCs detection such as

electrical conductivity[1,2]

mass transduction[3,4]

, surface acoustic wave[5]

optical variation in the physical properties of the sensing elements[6]

. In

the last case optical detection of gases are based on the change in the

optical properties of thin films (e.g. refractive index, extinction

coefficient, thickness, absorption, … etc.) due to the interaction of the

sensing layer with the molecules of the gas.

In this investigation we will consider some VOCs which are of

interest in food analysis. In particular those compounds with a well-

known toxicity such as amines. Alcohols are also present in flower and

fragrances related to many food products and involved in fats

deterioration processes.

Moreover, these chemicals were possible to be prepared in the form

of thin films using different chemical deposition techniques like casting,

spin coating, Langmuir-Blodgett, or physical technique like thermal

evaporation[7-20]

.

Synthesis of Some Vanillin Derivatives and their Use…

119

Experimental

Melting points were recorded on a Thomas-Hoover capillary melting

apparatus without correction. IR spectra were taken as KBr disks on a

Nicolet Magna 520 FTIR spectrometer. NMR spectra were obtained with

a Bruker DPX 400 (400MHz) spectrometer using CDCl3 solutions. UV-

visible spectra were recorded on a Shimadzu 1650 PC spectrometer for

solutions.

Materials

Vanillin, malononitrile, ethyl cyanoacetate, barbituric acid, thieob-

arbituric acid, indan1, 3-one, N,N-diethylthieobarbituric acid, and all

other solvents and reagents were purchased from Across chemicals and

used without any further purification.

General Procedure

A solution of vanillin (1.0g, 6.58 mmol) and an equivalent amount of

the active methylene compounds (6.58 mmol) in ethanol (10mL) was

wormed before addition of diethylamine (2 drops). After the addition was

completed the reaction mixture was refluxed for 1-2 hours, cooled to

room temperature and the precipitate product was collected by filtration

and dried. The physical and spectral data of the synthesized compounds

are given in Tables 1, 2 and 3.

Table 1. Physical data for vanillin dyes 1-6.

MF % of yield m.p./ °C Dye no.

C11H8N2O2 16.73 % 120ºC 1

C13H13NO4 84.92 % 50ºC 2

C12H10N2O5 87.20 % 270ºC 3

C12H10N2O4S 56.34 % 220ºC 4

C16H18N2O4S 11.83 % 120ºC 5

C17H12O4 60.26 % 185ºC 6


120

Table 2. H-NMR data of vanilins 1-6.

Table 3. IR Spectral data of vanillin dyes 1-6.

Results and Discussion

Synthesis of Dyes 1-6

Dyes 1-6 were prepared using knovenagel condensation as shown in

Scheme 1. The dyes 1-6 were characterized using different spectroscopic

techniques such as H1-NMR, FT-IR. The H1-NMR data are summarized

in Table 2. the most significant proton signal of these dyes is the signal of

olifinic protons which centered in the range of 7.96-8.84 ppm. The large

δ(ppm) / CDCl3 as solvent Dye no.

3.92 (3H, s, CH3O), 6.97-7.00 (1H, d), 7.33-7.35 (1H, d), 7.66-7.72 (1H, d), s

8.01 (1H, s, Olefinic Proton) 1

1.23-1.39 (3H,t, CH3), 3.72 (2H, q, CH2O), 4.01 (3H, s, CH3O), 5.63 (1H, s,

OH), 6.58-6.63 (1H, d), 6.846.86 (1H, d), 6.99-7.02 (1H, d) , 8.46 (1H, s,

Olefinic Proton).

2

3.88 (3H, s, CH3O), 5.2 (1H, s , OH), 7.03 (1H, d), 7.26 (1H, d), 7.31 (1H, d),

7.96 (1H, s, Olefinic Proton). 3

3.98 (3H, s), 4.40 (1H, s, OH), d 6.99-7.01 (1H, d), 7.385-7.388 (1H, d),

7.852-7.855 (1H, d) , 8.14 (1H, s, Olefinic Proton). 4

1.25 (6H, t, CH3CH2 ), s 3.29 (4H, q, CH3CH2-), 3.94 (3H, s, CH3O), s 5.94

(1H, s, OH), 6.63 (d, 1H), s 7.74 (d, 1H), 7.99 (d,1H) , 8.42 (1H, s, Olefinic

Proton).

5

3.93 (3H, s, CH3O), 5.21 (1H, s, OH), 6.97-6.99 (1H, s), 7.64-7.68 (1H, s),

7.77 (1H, s), 7.81-7.83 (2H, d), 7.93-7.99 (2H, d), 8.84 (1H, s, Olefinic

Proton).

6

υ/cm-1 Dye no.

3345.5, 2212, 2226, 1571, 1193, 1028.6, 1193 1

3447, 2232 , 1621.9, 1210.1, 1035.7, 1108.7, 1210.1 2

3277.9, 1666.4, 1746.3, 1178.6, 1010.4, 1178.6 3

3373.2, 3562.2, 1581.8 , 1024.7, 1219.4 4

3355, 1631.3, 1203.1, 1032.8,1133.6&1203.1 5

3451.9, 3553.3, 1667, 1570.6, 1152.1, 1198.3, 1664.4, 1708.8, 1020.3, 1092.9,

1152.1, 1198.3 6


121

chemical shifts of this signals depends on the strength of the electron

withdrawing groups, and also depends on the rigidity of such electron

withdrawing moieties which shield the olifinic protons in different ratio.

Table 3 summarizes the FT-IR data of dyes 1-6. One significant

absorption which common for all dyes is the stretching absorption bands

for OH which located in the region of 3278-3452 cm–1

. Other bands are

cyano stretching at 2232 cm–1

for dye 2.

Scheme 2

Scheme 1

Assessment of Sensing Properties of the Synthesized

Dyes 1-6 against Volatile Organic Amines

Sensing of Diethyl Amine (DEA) and Triethyl Amine (TEA)

The importance of this paper comes from the fact that, sensors are

sophisticated technology and expensive to acquire. This paper aims to

present a simple sensor system which can be effective in simple way and

can be judged visually by naked eye in the places where we need to sense

some volatile organic materials.

The simple sensing mechanism is based on the fact that, the

hydroxyl group of the vaniline is acidic and it can react with bases such

as organic amines or any material with basic nature, to produce oxonium


122

anion (Scheme 2), which is coloured. The colour of the oxonium ion

depends on the nature of the acceptor present. Figures 1-5 represent the

sensing of diethyl amins and Fig. 6 represents sensing of triethyl amine in

ethanol at various amounts of the amine.

Scheme 2

Fig. 1. UV – visible spectra of vanilin 1 in ethanol at various amounts of DEA.

Fig. 2. UV – visible spectra of vanilin 2 in vthanol at various amount of DEA.


123

Fig. 3. UV – visible spectra of vanilin 3 in ethanol at various amount of DEA .

Fig. 4. UV – visible spectra of vanilin 4 in ethanol at various amount of DEA.

Fig. 5. UV – visible spectra of vanilin 5 in ethanol at various amount of DEA.


124

Fig. 6. UV – visible spectra of vanilin 6 in ethanol at various amount of TEA.

Construction of Simple Sensor Device

A simple sensor device based on this approach was made by casting

the vaniline dye on a substrate such as glass or paper, after drying the

casting solvent, the device is ready for use. Exposing the device to the

vapor of the Amines gave a colour change from yellow to deep red in the

case of dye 1. The other dyes showed the same color change and the

colour formed depends on the dye.

Conclusion

The Vanillin dyes 1-6 prepared in this paper are potential candidates

to be used as sensors for amines and some other materials with basic

nature.

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